100% disabled Mom needs to get into a home. Where do we start?

Does she own her home ? She can stay in the home with professional care givers or go to a care facility and it can be generously paid for by renting the home.

Get Elder Care & Adult Protective Services in your area involved.

If you MIL and FIL did not have any money, an assets such as a home, savings accounts, stocks or bonds, then she should be able to qualify for Medicaid if you can show that she did not have all of those assets.
And, yes, most of the time Medicaid will require a five year look back, but not always. Accumulate as many of the documents that you can from her home and as far back as you can go. If you are honest and are able to show the caseworker what their situation was then they don't typically look back that far. For both my mom and my dad it was 6 months, because they didn't have any assets except for their home and a car. It all depends on their financial situation.
If she does have a home, it will more than likely need to be sold, then the profits, if any, will need to be used toward her nursing care. Once that is used up, then the nursing home will typically help you go through what needs to be done to apply for Medicaid. My father was in a skilled nursing home and the advocate helped me go through the process and they were very helpful.
My advice is to not panic. To get as much paperwork together as you can while she is mentally able to do so. Get a durable power of attorney in place by seeing an elder law attorney. They can also help you with the Medicaid process and the VA process.
Best of luck to you.

If your MIL has no assets she can go on Medicaid. Investigate nursing homes in your area and see if one can take her -- they will help you with the paperwork and tell you what documents you need to submit [Medicaid is retroactive]. Most of her social security aside from about fifty dollars will then go to Medicaid/the nursing home. If no beds are available, try putting her in the hospital, as if is often easier to transfer a person to a nursing home from a hospital than from home. As noted, if her husband was a vet definitely call the VA and see what if anything they might be able to do. Good luck!

You start with your county social services, office of the aging. You apply for Medi-Cal and they want five years of financial records to examine. If her husband was a wartime vet, you call the VA too.